In Vitro & In Vivo
Many scientific paper refer to the way they have studie something as ‘in vitro’ or ‘in vivo’. What do these terms mean? What are the differences (with regards to research)? And what is an example of their use?
In vitro studies are usually done with just a few cells in a controlled environment like a test tube or laboratory dish. In vitro is Latin for ‘within the glass’. This way researchers can look very specifically at only one process (and get more detailed results). Because of the relatively low costs and complexity, you can do many different experiments at low cost.
A downside is that in vitro studies may forgo the necessary complexity and ‘normal’ conditions that arise within a living organism. This is also called the absence of biokinetics: (the study of) the growth changes and movements that developing organisms undergo.
Examples of studies are those in microorganisms, cells, or biological molecules (proteins, DNA, RNA). For instance, you could study how RNA molecules bind to specific ligands (ion or molecule).
To better extrapolate from in vitro to in vivo you can do apply multiple techniques. You could increase the complexity of the in vitro system. Or you can use mathematical modelling to simulate a more complex system.
In vivo studies are done in living organism. In vivo is Latin for ‘within the living’. An in vivo study can be done in animals (including humans), and plants. This way researchers can see the real-life effects of drugs and interventions. This could show that the effect doesn’t take place, or that other (negative) side-effects happen. The costs are higher than for in vitro, but you get a much more realistic experiment.
An example of an in vivo study is to see if the body actually absorbs the molecule or treatment. If it passes through your body without getting picked up, then modifications should maybe be made.
In vivo experiments are done in many different species. Of them the mouse is one of the best known. The roundworm c. elegans is another much used test subject. Of course in vivo experiments are also done on humans. Because each animal is different (had different metabolic processes) it doesn’t mean that something that works in vivo on one, does also work in the other.
How do they translate?
Not all experiments that yield the desired result in vitro, translate to in vivo outcomes. One reason could be that the molecule or drug is not able to reach the destination you want it to work in, for instance, because it can’t breach the blood-brain barrier.
The same caveat also applies to the difference between different animals used in in vivo experiments.
Currently, I couldn’t find useful/any data on how many studies translate from in vivo -> in vitro (yeast) -> in vitro (mouse) -> in vitro (human) (of course extra steps can be added or removed). I hope to update this part soon.
In silico studies
These tests are performed on a computer (simulation). The Latin here is the same as the English: silicon (chips). Although quite new, in silico techniques could help to find out how drugs interact with the body and with pathogens. Three ways this technique could be applied are:
- Bacterial sequencing techniques – sequencing bacterial DNA and RNA to identify bacteria
- Molecular modelling – how drugs interact with the nuclear receptors of cells
- Whole cell simulations – simulating how a (bacterial) cell behaves in an environment